The present invention relates to a diaphragm pump including a driving shaft fixed, in a tilting state, to a rotating crank body.
A diaphragm pump of this type is described in, for example, Japanese Patent Laid-Open No. 2014-196679 (literature 1). The diaphragm pump described in literature 1 includes a crank body fixed to the rotating shaft of a motor, a driving body connected to the crank body via a tilting driving shaft, a diaphragm connected to the driving body, and a suction valve and a discharge valve.
The crank body is located on the same axis as the rotating shaft of the motor. The driving shaft is fixed to the crank body in a state in which one end on the crank body side is decentered with respect to the axis of the rotating shaft of the motor, and the other end approaches the axis of the rotating shaft. The driving body includes a shaft portion connected to the driving shaft, and a plurality of arm portions extending from the shaft portion outward in the radial direction.
The shaft portion is formed by a bearing member including a shaft hole in which the driving shaft is rotatably fitted, and a boss that stores the bearing member. The shaft hole is a non-through hole that opens at one end of the bearing member facing the crank body.
An oil storage groove opening to the shaft hole is formed in the bearing member. The oil storage groove is filled with lubricating oil to lubricate a slidable contact portion between the driving shaft and the bearing member. The oil storage groove extends along the shaft hole in parallel to the axis of the driving shaft and opens to the other end of the bearing member. For this reason, the inner peripheral surface (a sliding surface on which the distal end of the driving shaft slides) of the closed-side end of the shaft hole located on the other end side of the bearing member is interrupted by the oil storage groove in the circumferential direction.
A deformed portion of the diaphragm is attached to each arm portion of the driving body. The deformed portion forms a part of the wall of a pump chamber. In the diaphragm pump disclosed in literature 1, when the crank body rotates together with the rotating shaft of the motor, the driving body converts the rotation into a reciprocal motion, thereby contracting or expanding the deformed portion. When the pump chamber contracts, the discharge valve opens and discharges a fluid in the pump chamber. On the other hand, when the deformed portion expands, the suction valve opens, and the fluid is sucked into the pump chamber.
As described above, the oil storage groove opens to the closed-side end of the shaft hole. For this reason, the circularity of the closed-side end lowers. When the circularity is low, the surface pressure of the contact portion between the shaft hole and the driving shaft is difficult to be constant. As a result, when the distal end of the driving shaft slides in the shaft hole while receiving the load of the pump, an oil film is interrupted at a portion where the surface pressure of the sliding portion becomes high, and wear progresses. For this reason, in the diaphragm pump disclosed in literature 1, the wear resistance may be low.